Hunting living fossils on the ocean floor

WE WERE descending through the Caribbean sea in a tiny submarine. Our mission: to go down more than 200 metres to hunt for living fossils called stalked crinoids.

Crinoids are like upside-down starfish. But whereas starfish crawl over the sea floor, their relative, the crinoid, is rooted to the bottom via a stalk. Crinoids - also known as sea lilies - thrust as many as 60 feathery arms upwards to strain plankton from the water. About 300 million years ago, when the seas were just a soupy mixture of plankton with no fish or mammals, the crinoid was king. But as their environment changed, extinction loomed.

Around 200,000 years ago, a new subclass evolved with the ability to move. There was an explosion of new species, and most of the stalked, stationary ancestors became extinct. Shale beds - the muddy bottoms of ancient seas turned to rock - are covered ...

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